The basic objectives of the Project, now in its fourth year, are threefold: a) to fuse a gas chromatograph, a low resolution mass spectrometer, and a gas flow proportional counter into a single computer-controlled unit (GPM unit) which could identify each component in a cell extract, assay to level of occurrence, and determine the amount of radioactivity it contained, b) to apply the methods of compartmental analysis to biosynthetic incorporation experiments, and c) to use such a technology to track the metabolism of a specific substance added to the cells. It was argued that this approach would allow pathways of both intermediary and secondary metabolism to be treated as units rather than arbitrary groupings of isolated reactions. Parameters descriptive of in vivo enzyme activity would be forthcoming as would measures of the relative activities of competing and parallel-running pathways. Such an outcome would have major impact on the fields of enzymology, cellular nutrition, drug action and metabolism, cell differentiation and gene expression. As a model system the Project is focusing on the process whereby the anti-tumor drug, mycophenolic acid, is produced by the fungus Penicillium brevicompactum. Four intermediates in the pathway have already been identified in cell extracts. Work is continuing to determine the extent to which the mycophenolic acid biosynthetic pathway competes for carbon with the other acetate-dependent pathways of the cell. It is hoped that such information will shed light on the function of fungal secondary metabolism.